Effective Connectivity Measured Using Optogenetically Evoked Hemodynamic Signals Exhibits Topography Distinct from Resting State Functional Connectivity in the Mouse

Abstract

Brain connectomics has expanded from histological assessment of axonal projection connectivity (APC) to encompass resting state functional connectivity (RS-FC). RS-FC analyses are efficient for whole-brain mapping, but attempts to explain aspects of RS-FC (e.g., interhemispheric RS-FC) based on APC have been only partially successful. Neuroimaging with hemoglobin alone lacks specificity for determining how activity in a population of cells contributes to RS-FC. Wide-field mapping of optogenetically defined connectivity could provide insights into the brain’s structure–function relationship. We combined optogenetics with optical intrinsic signal imaging to create an efficient, optogenetic effective connectivity (Opto-EC) mapping assay. We examined EC patterns of excitatory neurons in awake, Thy1-ChR2 transgenic mice. These Thy1-based EC (Thy1-EC) patterns were evaluated against RS-FC over the cortex. Compared to RS-FC, Thy1-EC exhibited increased spatial specificity, reduced interhemispheric connectivity in regions with strong RS-FC, and appreciable connection strength asymmetry. Comparing the topography of Thy1-EC and RS-FC patterns to maps of APC revealed that Thy1-EC more closely resembled APC than did RS-FC. The more general method of Opto-EC mapping with hemoglobin can be determined for 100 sites in single animals in under an hour, and is amenable to other neuroimaging modalities. Opto-EC mapping represents a powerful strategy for examining evolving connectivity-related circuit plasticity.

Large Scale Double-Path Illumination System with Split Field of View for the All-Optical Study of Inter-and Intra-Hemispheric Functional Connectivity on Mice

“…Moreover, the cortical propagation that was observed for the selected ROIs resembles the spatial correlation of axonal projections, as observed in previous studies [23,35]. These results confirm that axonal projection structures, as observed in the Allen Mouse Brain Connectivity Atlas (AMBCA, [36]), were related to cortical function.…”

In vivo voltage-sensitive dye imaging of mouse cortical activity with mesoscopic optical tomography

“…[51][52][53] Within the brain, ChR2-positive cells appear in large pyramidal neurons in cortical layer 5, CA1 and CA3 pyramidal neurons in the hippocampus, mossy fibers in the cerebellum, and neurons in various regions of the thalamus, midbrain, and lower brainstem as previously reported. 51,53 Within the cortex, ChR2 is mainly expressed in both axons and dendrites of the layer 5 pyramidal neurons that have pronounced apical dendritic tufts in layers 1 and 2/3. 18,[51][52][53][54] Also, it has been shown that ChR2 expression varies <50% across the anterior-posterior axis within layer 5.…”

“…These Thy1-ChR2-YFP transgenic mice express the light-activated ion channel, channelrhodopsin-2 (from the green algae Chlamydomonas reinhardtii), fused to yellow fluorescent protein (ChR2-YFP) under the control of the mouse thymus cell antigen 1 (Thy1) promoter. [51][52][53] The spatial distribution of ChR2 in the Thy1 mouse line has been well characterized in several previous studies. [51][52][53] Within the brain, ChR2-positive cells appear in large pyramidal neurons in cortical layer 5, CA1 and CA3 pyramidal neurons in the hippocampus, mossy fibers in the cerebellum, and neurons in various regions of the thalamus, midbrain, and lower brainstem as previously reported.…”

“…[51][52][53] The spatial distribution of ChR2 in the Thy1 mouse line has been well characterized in several previous studies. [51][52][53] Within the brain, ChR2-positive cells appear in large pyramidal neurons in cortical layer 5, CA1 and CA3 pyramidal neurons in the hippocampus, mossy fibers in the cerebellum, and neurons in various regions of the thalamus, midbrain, and lower brainstem as previously reported. 51,53 Within the cortex, ChR2 is mainly expressed in both axons and dendrites of the layer 5 pyramidal neurons that have pronounced apical dendritic tufts in layers 1 and 2/3.…”

Optogenetic study of the response interaction among multi-afferent inputs in the barrel cortex of rats

“…Optical stimulation using optogenetics has advantages over other artificial inputs, such as electrical stimulation, because of its high spatiotemporal precision 1–5 , enabling targeted expression of the light-gated ion channels and targeted irradiation with a given spatiotemporal pattern. Recently the circuit specificity involved in the motor behavior 6–10 , the interregional cortical connectivity 11–14 , and the primary visual cortical responses 15 have been successfully mapped in the brain of a rodent in vivo using optogenetics to stimulate cerebral neurons in combination with behavioral outputs, electrophysiological recordings, optical measurements and/or fMRI 16–18 . However, the cortical response is not merely a summation of the input signals.…”